Known as a conventional adsorption sensor is a sensor capable of detecting a trace of NO2 gas by utilizing a reduction in the oscillation frequency of a crystal oscillator in accordance with the NO2 gas adsorbed on a gas sensitive film as disclosed in Patent Literature 1.
As disclosed in Patent Literature 2, there is known a method of detecting adsorption of a substance by utilizing absorption of an evanescent field, generated by waveguiding light to a waveguide path, by an adsorption substance, and attenuation of the waveguided light.
As disclosed in Patent Literature 3, there is also known a method of depositing a metallic thin film on a waveguide path, utilizing attenuation of waveguided light when a surface plasmon is excited on the metallic thin film by the waveguided light, utilizing a change in the excitation condition of the surface plasmon with adsorption of a substance to be measured, and measuring outgoing light, thereby detecting adsorption of the substance.    Patent Literature 1: Unexamined Japanese Patent Publication No. H7-43285    Patent Literature 2: Unexamined Japanese Patent Publication No. H9-61346    Patent Literature 3: Unexamined Japanese Patent Publication No. 2001-108612